Here is a brief intro to the historic marker.Composed of
limestone or “Selma chalk” which abounds in fossils.
Called “Ecor Blanc” by eighteenth-century French
explorers and cartographers. Named “Chickasaw Gallery”
because early Indian inhabitants harassed boats from here. Landing
site of Bonapartist exiles who established the “Vine and
Olive Colony” in 1817.
The very first question that comes to mind when looking across
the river and see the Selma chalk beds is what is chalk? Well Selma
chalk or Marl is define as the following:is a soft, white, porous
sedimentary rock, a form of limestone composed of the mineral
calcite. Calcite is calcium carbonate . It forms under relatively
deep marine conditions from the gradual accumulation of minute
calcite plates (coccoliths) shed from micro-organisms called
coccolithophores. It is common to find chert or flint nodules
embedded in chalk. Selma Chalk can also refer to other compounds
including magnesium silicate and calcium sulfate.Selma Chalk is
resistant to weathering and slumping compared to the clays with
which it is usually associated, thus forming tall steep cliffs
where chalk ridges meet the sea. Chalk hills, known as chalk
downland, usually form where bands of chalk reach the surface at an
angle, so forming a scarp slope. Because chalk is porous it can
hold a large volume of ground water, providing a natural reservoir
that releases water slowly through dry seasons.
Downland is formed when chalk formations are raised above the
surrounding rocks. The chalk slowly erodes to form characteristic
rolling hills and valleys. As the Cretaceous chalk layer in
southern Alabama is typically tilted, chalk downland formations
often have a marked scarp slope on one side, which is very steep,
and a dip slope on the other, which is much shallower. Where the
downs meet the sea, characteristic white chalk cliffs form, such as
the one you see at the river bed in front of you. The soil profile
of chalk downland in Alabama is a thin soil overlaying the parent
chalk. Unlike many soils in which there are easily distinguished
layers or soil horizons, a chalk rendzina soil consists of only a
shallow dark humus rich surface layer which grades through a
lighter brown hillwash containing small pellets of chalk, to the
white of the chalk itself. This is largely because of the purity of
the chalk which is here about 98% calcium carbonate and the
consequent absence of soil-building clay minerals which are
abundant, for example, in valley floors as the one here.
Chalk deposits are very porous, so the height of the water table
in chalk hills rises in winter and falls in summer. This leads to
characteristic chalk downland features such as dry valleys or
coombes, and seasonally-flowing streams or winterbournes. In the
valleys below the downs there is typically a clay soil, and at the
interface between the two a springline can occur where water
emerges from the porous chalk. Along this line, settlements and
farms were often built, as on the higher land no water was
available
Question to be answered?
1.) What color of chalk do you?
2.) What Variety of other minerals do you?
3.) What is the width of bands of chalk you see?